Physics of helicon discharges

Chen, Francis F.

doi:10.1063/1.871697

Cited by 142 publications

(112 citation statements)

References 17 publications

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“…The pressure is measured with a capacitive pressure gauge. As RF antenna a Nagoya-type Helicon antenna which couples to the |m| = 1 Helicon modes is applied [4]. The antenna is connected to the RF generator (13.56 MHz, max.…”

Section: Experimental Setup and Diagnostic Methodsmentioning

confidence: 99%

“…If the pressure can be reduced, the over-all efficiency of the NNBI system could be increased as the stripping losses of H − due to collisions with the gas would be reduced. Furthermore, more smoother radial profiles of the plasma parameters are expected with Helicon coupling since the coupling mechanism is based on wave heating of the plasma volume [4] not on collisional heating within the skin depth.…”

Section: Introductionmentioning

confidence: 99%

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Investigation of Helicon discharges as RF coupling concept of negative hydrogen ion sources

Briefi

Fantz

2013

AIP Conference Proceedings

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Abstract. The ITER reference source for H − and D − requires a high RF input power (up to 90 kW per driver). To reduce the demands on the RF circuit, it is highly desirable to reduce the power consumption while retaining the values of the relevant plasma parameters namely the positive ion density and the atomic hydrogen density. Helicon plasmas are a promising alternative RF coupling concept but they are typically generated in long thin discharge tubes using rare gases and an RF frequency of 13.56 MHz. Hence the applicability to the ITER reference source geometry, frequency and the utilization of hydrogen/deuterium has to be proved. In this paper the strategy of the approach for using Helicon discharges for ITER reference source parameters is introduced and the first promising measurements which were carried out at a small laboratory experiment are presented. With increasing RF power a mode transition to the Helicon regime was observed for argon and argon/hydrogen mixtures. In pure hydrogen/deuterium the mode transition could not yet be achieved as the available RF power is too low. In deuterium a special feature of Helicon discharges, the socalled low field peak, could be observed at a moderate B-field of 3 mT.

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Section: Experimental Setup and Diagnostic Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Investigation of Helicon discharges as RF coupling concept of negative hydrogen ion sources

Briefi

Fantz

2013

AIP Conference Proceedings

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show abstract

“…The discharge vessel is made out of quartz glass, has a length of 40 cm, a diameter of 10 cm and is attached to the vacuum system at the ends of the cylinder. As RF antenna a Nagoya-type Helicon antenna which couples to the |m| = 1 Helicon modes is applied [11]. The antenna is connected to the RF generator which operates at a frequency of 13.56 MHz via a matching network.…”

Section: Helicon Couplingmentioning

confidence: 99%

Alternative RF coupling configurations for H− ion sources

Briefi

Gutmann

Fantz

2015

AIP Conference Proceedings

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Abstract. RF heated sources for negative hydrogen ions both for fusion and accelerators require very high RF powers in order to achieve the required H − current what poses high demands on the RF generators and the RF circuit. Therefore it is highly desirable to improve the RF efficiency of the sources. This could be achieved by applying different RF coupling concepts than the currently used inductive coupling via a helical antenna, namely Helicon coupling or coupling via a planar ICP antenna enhanced with ferrites. In order to investigate the feasibility of these concepts, two small laboratory experiments have been set up. The PlanICE experiment, where the enhanced inductive coupling is going to be investigated, is currently under assembly. At the CHARLIE experiment systematic measurements concerning Helicon coupling in hydrogen and deuterium are carried out. The investigations show that a prominent feature of Helicon discharges occurs: the so-called low-field peak. This is a local improvement of the coupling efficiency at a magnetic field strength of a few mT which results in an increased electron density and dissociation degree. The full Helicon mode has not been achieved yet due to the limited available RF power and magnetic field strength but it might be sufficient for the application of the coupling concept to ion sources to operate the discharge in the low-field-peak region.

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“…They reported the surface current required at the boundary of the plasma needed to match the plasma wave field to the vacuum wave field. Chen 12 identified that the surface current was associated with a pseudosurface wave. Chen predicted the existence of pseudosurface waves in a helicon wave device at low B field and a wave propagation mode change between a͒ pseudosurface waves and helicon waves under certain conditions.…”

Section: Introductionmentioning

confidence: 99%

Azimuthally symmetric pseudosurface and helicon wave propagation in an inductively coupled plasma at low magnetic field

et al. 1998

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The mode transition from a capacitively coupled mode ͑E mode͒ to an inductively coupled mode ͑H mode͒ was observed in an inductive Ar plasma source by applying an axially uniform low B field. The applied fundamental rf was 13.56 MHz and many harmonic components were observed. A beat and standing wave patterns of azimuthally symmetric (mϭ0 mode͒ first and second harmonic pseudosurfaces and helicon waves were measured at various densities (nϳ9.0ϫ10 10 -2.2 ϫ10 11 cm Ϫ3 ) and B fields ͑12-28 G͒. Wave propagation mode changes, from pseudosurface to helicon waves and from helicon to pseudosurface waves, were observed at critical conditions, c / Ͼ3.0 and nϳ2.2ϫ10 11 cm Ϫ3 .

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Physics of helicon discharges

Cited by 142 publications

References 17 publications

Investigation of Helicon discharges as RF coupling concept of negative hydrogen ion sources

Investigation of Helicon discharges as RF coupling concept of negative hydrogen ion sources

Alternative RF coupling configurations for H− ion sources

Azimuthally symmetric pseudosurface and helicon wave propagation in an inductively coupled plasma at low magnetic field

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